KEY POINTS:
A new fertility test will be no "magic bullet" for women hoping to conceive, experts say.
The test that measures the levels of Anti-Mullerian Hormone (AMH) in a woman's blood, pointing to the number of eggs she has left, has caused controversy in other countries where it has been said to falsely raise women's hopes.
Fertility experts in Australia raised concerns this year that the test did not take into account lifestyle factors that could inhibit a woman's chances of conceiving, such as weight, smoking and alcohol consumption.
Experts in New Zealand have also sounded a note of caution.
Lynda Williams, co-ordinator of Auckland Women's Health Council, said the test gave women a "false sense of security" about having children.
"It purports to give a woman certainty and knowledge and reassurance about planning to have their children that is just false.
"It's really misguided for women to think they have that much knowledge and control over when they can have a baby."
Richard Fisher, Fertility Associates director, said that used in conjunction with Follicle Stimulating Hormone (FSH), AMH was a "useful additional test" of a woman's fertility but lifestyle factors must also be taken into account.
"There are many things that will have a greater influence on somebody's reproductive potential than just AMH and some of those will be about weight and smoking and lifestyle and they'll probably have a much greater influence than the hormone," he said. "It's not a magic bullet."
Fertility Associates, along with Diagnostic Medlab, has completed an initial series of tests to validate the test for a New Zealand population.
The tests are widely available in Australia, Britain and the United States.
In Britain, a "traffic light" system is used to measure fertility. Green meant AMH levels were normal and there should be no trouble conceiving for another year at least.
Amber meant that AMH levels were starting to fall and there might be problemsconceiving if it was delayed by more than a year.
Red meant levels were low and the woman might already be menopausal.
Dr Fisher said that for women undergoing treatment like IVF, requiring stimulation of the ovary with drugs, AMH could help them decide whether to begin treatment.
For others it could be about choosing the correct dosage of drugs to avoid over-stimulation.
Until now, doctors in New Zealand have tested only for FSH, whose levels rise when the ovaries stop producing enough oestrogen to maintain normal ovarian function.
Statistics out yesterday suggested thousands of New Zealand women could be booking themselves in for a test.
Statistics New Zealand said figures for the year to September confirmed the trend of women having babies well into their30s.
In the September 2008 year, women aged 30-34 had the highest fertility rate (127 births per 1000).
Forty years ago, in 1968, women aged 20-24 had the highest fertility rate (218 per 1000), almost three times their 2008 rate (78 per 1000).
WHAT IS AMH?
* A hormone produced in women's ovaries and men's testes.
* Women's levels rise slowly until adulthood when they begin a persistent decline throughout reproductive life.
* AMH disappears at menopause.
* It can be measured with a blood test at any time in the menstrual cycle or when on oral contraceptives.
WHAT DOES IT COST?
* Publicly funded options are available if referred by a GP. Privately funded initial consultations depend on the clinic, but are typically around $200.
* The test itself costs $45-$50.
